The invention is based on a fuel injection pump as defined hereinafter. A fuel injection pump of this kind is already known from German Patent Application 29 23 445 A.
In fuel injection pumps, the following problem arises: If the pumping rate of the fuel injection pump is optimized to the rated output point of the internal combustion engine at maximum load and maximum rpm, so that the maximum allowable pressure in the pump work chamber of the fuel injection pump occurs, then this pressure is as a rule overly low, given a low rpm of the fuel injection pump or of the associated engine, at the lower full-load point, for the sake of the quality of fuel introduction into the engine combustion chambers through injection valves. If the pumping rate is raised in this range, then although the pressure at this lower full-load point then desirably rises, nevertheless, at the rated power point the fuel injection pump is overloaded. Accordingly, if the pressure at the lower full-load point is raised, then provision must be made so that the pump will not be overloaded at the rated power point.
The aforementioned known fuel injection pump discloses a device with which the pumping rate is reduced in the lower load/rpm range as a function of the feeding in full-load operation and at high rpm, in order to achieve noise-abating long injection times or low injection rates with respect to the injection quantity. Then the work chamber upstream of the adjusting piston is supplied continuously with pressure fluid, brought to an rpm-dependent pressure, from a pressure fluid source for the sake of rpm-dependent adjustment of the adjusting piston and hence of the onset of high-pressure pumping by the pump piston, and the withdrawal device is put into operative connection with the work chamber upstream of the adjusting piston as a function of the rpm.